The objective of this research is to delineate antigens of possible significance to the pathogenesis of rheumatoid arthritis (RA). Many cell lines of RA synovial, dermal and normal synovial fibroblasts have been grown in culture and are stored under liquid nitrogen. Antigens unique to the RA-derived synovial fibroblasts are being delineated by the immunological technique of making anti-RA synovial fibroblast sera specific for the RA cells by absorption with the RA dermal and normal synovial fibroblasts. Tissue-specific antigens have been and RA-specific antigens will be defined by the indirect immunofluorescence and the mixed cell agglutination reactions. Incubation of minced synovial tissue with radiolabeled amino acids has been used to obtain radiolabeled biosynthesized antibody. This antibody has been isolated from from other labeled macromolecules using immunoabsorbent columns of anti-human Ig conjugated to Sepharose. The antibody isolated is quantitated by immunopreciplitation and the amounts of rheumatoid factor activity determined by absorptions to latex-bound human Ig. The radiolabeled antibody shows a differential binding to RA synovial fibroblasts compared to dermal cells. The specificity of this reaction is being further tested as well as the determination of the nature of the antibody that binds to the cells. In addition, the chemical nature of the antigen(s) involved in this reaction will be studied.